1. Field of the Invention
This invention relates to a keyboard device for an electronic musical instrument, such as an electronic piano and an electronic organ.
2. Prior Art
In general, a keyboard device for an electronic musical instrument includes a key switch arranged beneath each key thereof for detecting depression of the key. The electronic musical instrument produces a musical tone based on results of detection of the keys status of each key by the key switch associated therewith. Further, the keyboard device is classified into a hammer type having a hammer associated with each key for being swung thereby to make the sense of a touch on the key similar to that obtained from an acoustic piano, and a hammerless type having no such hammers.
Of the two types of keyboard device, the hammer type is disclosed e.g. by Japanese Provisional Patent Publication (Kokai) No. 2-149893. The proposed hammer-type keyboard device is provided with keys each having a rear portion thereof supported on a pivot for rotation thereabout, and a switch-depressing projection formed on a lower side surface thereof for depressing a key switch provided at a location away from the pivot by approximately half the length of the key. Further, this keyboard device includes a keyboard chassis having key switches each formed by a rubber switch and located just beneath a corresponding switch-depressing projection for being directly depressed by the switch-depressing projection when a player depresses a key corresponding thereto. On the other hand, hammers are each rotatively supported on pivots other than those for the keys. Each of the hammers has a projection formed thereon on the side forward of its pivot at a location away from the pivot of the corresponding key by approximately one third of the length of the key, for abutting on the lower side surface of the key. As the key is depressed, the hammer is directly driven by the key into swinging motion around its pivot.
However, the conventional keyboard device has room for improvement in respect of the following points:
First, in spite of provision of hammers, the keyboard device cannot offer the sense of a touch on each key which is sufficiently similar to that obtained from an acoustic piano. This is because unlike the acoustic piano in which each hammer strikes a string to produce a musical tone, the conventional keyboard device for the electronic musical instrument has the switch-depressing projection provided for directly operating the key switch, that is, the conventional keyboard device is not constructed such that a musical tone is produced according to motion of each hammer, which sets a limit to realization of the sense of a key touch close to that obtained from the acoustic piano.
Secondly, if the conventional keyboard device is to be manufactured while permitting the common modifications of a hammer type and a hammerless type, the location of the key switch thereof is required to be shifted in a forward or backward direction depending on the type of the keyboard device. As already mentioned above, it is preferred for the hammer type that the key switch is operated by way of the hammer for the purpose of making the sense of a key touch closer to that obtained from the acoustic piano. On the other hand, in the conventional keyboard device, the hammer is arranged at a location fairly backward of the key switch, so that it is required to rearrange the key switch at a location suitable for receiving action of the hammer, if the key switch is to be operated by way of the hammer. Such a shift of the location of the key switch in a forward or backward direction between the hammer-type keyboard device and the hammerless-type keyboard device prevents compatibility of a key switch and fixture means thereof for one type of the keyboard device with those for the other type, which in turn prevents reduction of manufacturing cost thereof. Further, when the key is depressed, the resilient force of the key switch acts on the key as a reaction force, so that if the key switch is shifted to a forward or backward location depending on whether or not the hammer is provided, the characteristic of depressing load of the key is largely changed.
Further, in the conventional keyboard device, the hammer is provided with a projection which directly abuts on the lower side surface of the key, for being depressed thereby. This makes the configuration of a contact surface of the hammer complicated, resulting in inconveniences, such as limitation of the kind of cushion material normally attached to the contact surface of the hammer.